1. Field of the Invention
The present invention relates to a steering damper provided in a steering wheel of a motor cycle or the like, or a rotary damper preferably used in a suspension damper or the like provided in a rear wheel suspension apparatus of the motor cycle or the like.
2. Description of the Related Art
As for the rotary damper, there are structures described in Japanese Patent No. 2593461, Japanese Patent Application Laid-open No. 2003-175877, and Japanese Patent Application Laid-open No. 2004-231036.
The rotary damper described in Japanese Patent No. 2593461 is structured, as shown in FIG. 12, such that a rotor 2 is provided within a casing 1, and first and second oil chambers 3A and 3B are sectioned in both sides of a vane of the rotor 2. The structure is made such that two oil chambers 3A and 3B are connected by a single oil passage 4, and a damping force generating apparatus 5 is interposed in the oil passage 4. The single oil passage 4 is used for every rotation of the rotor 2, and a damping force is generated by the single damping force generating apparatus 5.
The rotary damper described in Japanese Patent Application Laid-open No. 2003-175877 is structured, as shown in FIG. 13, such that two oil chambers 3A and 3B are sectioned in both sides of the vane of the rotor 2 within the casing 1, and these two oil chambers 3A and 3B are connected by two parallel oil passages 6A and 6B. A damping force generating apparatus 7 is interposed in a cross connection portion in which two oil passages 6A and 6B are crossed, and the respective oil passages 6A and 6B are provided with two check valves 8A to 8D. The different oil passages 6A and 6B are employed by changing the rotation of the rotor 2, and the damping force is generated by the single damping force generating apparatus 7.
Further, a rotary damper provided with a relief valve 30 is disclosed in Japanese Patent Application Laid-open No. 2004-231036 (FIGS. 3 and 5).
In this case, response is an important feature in the performance of a rotary damper. In the rotary damper of Japanese Patent No. 2593461, the single oil passage 4 is used in every rotation of the rotor 2, and an inertia force of the oil generated within the single oil passage 4 inhibits the response at a time when the rotation of the rotor 2 is changed.
In the rotary damper in Japanese Patent Application Laid-open No. 2003-175877, since the different oil passages 6A and 6B are used during changing the rotation of the rotor 2, the response can be improved by canceling the inertia force of the oil. However, since four check valves 8A to 8D are totally employed for setting the number of the damping force generating apparatus 7 to one, a cost increase is caused.
In the rotary damper in Japanese Patent Application Laid-open No. 2004-231036, since the relief valve 30 is provided within the housing 13, there is a problem that the size of the rotary damper is enlarged.